title: The EEG correlates of the TMS-induced EMG silent period in humans.
abstract: Application of magnetic or electrical stimulation to the motor cortex can result in a period of electromyography (EMG) silence in a tonically active peripheral muscle. This period of EMG silence is referred to as the silent period (SP). The duration of SP shows intersubject variability and reflects the integrity of cortical and corticospinal pathways. A non-invasive technique for assessing the duration of SP is the combination of Transcranial Magnetic Stimulation (TMS) with EMG. Utilizing TMS-EMG, several studies have reported on the shortening or lengthening of SP in neuropsychiatric disorders such as schizophrenia, bipolar disorder, depression, obsessive compulsive disorder, epilepsy, Parkinson's disease, and stroke. However, cortical, corticospinal and peripheral components are difficult to disentangle from EMG alone. Here, we use the multimodal neuroimaging technique of TMS-EMG combined with concurrent electroencephalography (EEG) recording to further examine the cortical origin of SP and the cortical oscillatory activity that underlies SP genesis. We demonstrate that the duration of SP is related to the temporal characteristics of the cortical reactivity and the power of delta to alpha oscillations in both local and remote areas ipsilateral and contralateral to the stimulation site, and beta oscillations locally. We illustrate that, compared to EMG, the EEG indices of the SP provide additional information about the brain dynamics and propose that the EEG measures of SP may be used in future clinical and research investigations to more precisely delineate the mechanisms underlying inhibitory impairments.
authors.affiliation: Berenson-Allen Center for Non-invasive Brain Stimulation, Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA. Electronic address: ffarzan@bidmc.harvard.edu.
authors.forename: Faranak
authors.initials: F
authors.lastname: Farzan
authors.forename: Mera S
authors.initials: MS
authors.lastname: Barr
authors.forename: Sylco S
authors.initials: SS
authors.lastname: Hoppenbrouwers
authors.forename: Paul B
authors.initials: PB
authors.lastname: Fitzgerald
authors.forename: Robert
authors.initials: R
authors.lastname: Chen
authors.forename: Alvaro
authors.initials: A
authors.lastname: Pascual-Leone
authors.forename: Zafiris J
authors.initials: ZJ
authors.lastname: Daskalakis
mesh_terms: D000328:Adult; D000513:Alpha Rhythm / Q000502:physiology; D001683:Biological Clocks / Q000502:physiology; D001931:Brain Mapping / Q000379:methods; D013181:Cortical Spreading Depression / Q000502:physiology*; D004569:Electroencephalography / Q000379:methods; D004576:Electromyography / Q000379:methods*; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D009044:Motor Cortex / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013223:Statistics as Topic; D050781:Transcranial Magnetic Stimulation / Q000379:methods*; D055815:Young Adult
keywords: Cortical inhibition; Cortical oscillations; Electroencephalography; Electromyography; GABA; Motor cortex; Transcranial magnetic stimulation